This invention relates to a refractory having excellent spalling resistance for use in casting a basic substance.
A castable refractory having magnesia as a main ingredient has long been used as a lining material for ladles, tundishes, vacuum degasing furnaces, mixers, etc. Such a refractory will hereinafter be referred to as a "basic casting material".
Basic casting materials have excellent resistance to erosion by highly basic slags and do not contaminate molten steel. Consequently, they are suitable for conversion of molten steel into clean steel. On the other hand, they suffer conspicuously from thermal spalling and structural spalling due to penetration of slag and therefore can not fully manifest the benefits expected of basic substances.
Various proposals have been made to solve the problem of spalling by basic casting refractories. The incorporation of carbon is basic casting materials having magnesia as a principal ingredient (Japanese Provisional Patent Publication No. 57-92,581), the incorporation of alumina (Japanese Provisional Patent Publication No. 60-60,986), the incorporation of silica in an amount not less than 80% by weight (Japanese Provisional Patent Publication No. 53-26,734), and the incorporation of chromium ore (Japanese Provisional Patent Publication No. 52-140,429) are examples of such proposals.
However, none of the above-mentioned proposals can be described as totally satisfactory. To be specific, the carbon-containing material suffers from inferior erosiono resistance due to oxidation of carbon. The addition of alumina causes spinel due to the reaction of alumina with magnesia and also causes cracks or exfoliation due to expansion. The incorporation of silica results in reduced erosion resistance due to formation of a MgO--SiO.sub.2 type substance with a low melting point due to the reaction of silica with magnesia. Chromium ore is not sufficiently effective at preventing slag penetration and results in extensive structural spalling.